Duplexing in automatic document feeder utilizing a path shorter than the length of the document to be duplexed

ABSTRACT

The footprint of a document scanning unit such as a copier, facsimile machine or document scanner or combinations thereof is reduced by causing overlap of the leading and trailing edges of long document sheets to be scanned in the document delivery roller system downstream of the scanning station. Differential slippage of the overlapping ends between a drive roller and a pinch roller is provided in a first embodiment. A second embodiment uses a moveable pinch roller in the document delivery system to selectively open and close a gap to permit slippage of the leading and trailing edges of the document. A third embodiment uses three document delivery rollers defining two spaced nips in which the leading and trailing edges of a long document are simultaneously present and a crenellated roller surface to guide the leading edge of the document to the desired nip in the delivery system.

CROSS REFERENCE TO RELATED APPLICATION(S)

This is a divisional of copending application Ser. No. 09/452,831 filedon Dec. 1, 1999.

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to the feeding of individual documentsheets to be scanned in a document scanner and, more particularly to thedocument delivery system which receives the scanned documents and, ifdesired, routes the individual sheets back to the scanning region forduplex scanning, i.e., scanning of both sides of the document sheet. Asused herein, the term “document scanning device” is intended to bebroadly defined to include, but not necessarily be limited to, standalone document copiers, facsimile machines, document scanning machinesand combinations of such units.

Automatic document feed and delivery systems in large copiers capable ofduplex scanning generally require a document feed path that is as longas the document that is to inverted during duplex scanning. While thisis not a great disadvantage in a large piece of multi-user officeequipment, in a small multi-function peripheral copier or scanningapparatus, it is of great impact on the footprint size of the apparatus.Large footprint size requires significant desk space which must be keptavailable. In such units, the length of the duplexing section aloneapproaches half of the document length. This is considerably large whenduplex scanning legal size documents for example. Other disadvantages ofa longer duplexing path are added cost due to additional rollers andguides to manage the extra length of media and the increased potentialof document jamming due to the increased complexity. One manner ofavoiding a long duplexing path is to eject the document outside theduplicating apparatus onto a tray which projects from the side of themachine. This solution also consumes space and has the addeddisadvantage of increased propensity for damage to the document while itis outside of the protective confines of the unit.

It is accordingly of considerable advantage to provide a more compactdocument scanning device by utilizing a more compact duplexing section.

SUMMARY OF THE INVENTION

The present invention provides a method of feeding and duplex scanning adocument in a document scanning device comprising the steps of:

a) transporting individual sheets of said document from a stack thereofto a scan region of a scanning system;

b) scanning a first face side of said document sheet at said scanregion;

c) transporting said sheet from said scan region to a pair of opposeddocument exit transport rollers;

d) gripping opposite face sides of said sheet in a nip between said exittransport rollers and rotating said exit transport rollers in an exitdirection to pull said sheet therebetween in an exit direction to move atrailing edge of said sheet away from said scan region;

e) reversing the direction of rotation of said exit transport rollersbefore said trailing edge of said sheet passes therebetween to feed saidsheet to said scan region in face inverted orientation for scanning asecond face side of said document sheet;

f) scanning a leading portion of said second face side of said sheet andtransporting a leading edge of said sheet to said nip between said exittransport rollers before a trailing edge of said sheet passes said nipin a feed direction to cause buckle formation in said sheet between saidnip and said scan region;

g) again reversing the direction of rotation of said exit transportrollers to rotate said exit transport rollers in said exit direction toconsume sheet buckle in said nip without causing differential slippageof adjacent leading and trailing portions of said sheet in said nip;

h) continuing to rotate a driven one of said exit transport rollers insaid exit direction to pull a trailing portion of said sheet to saidscan region and scanning said trailing portion of said second side ofsaid sheet while permitting said trailing portion of said sheet to slippast a leading portion of said sheet in said nip; and

i) rotating said exit transport rollers in said exit direction to ejectsaid sheet from between said transport rollers.

In apparatus terms, a first embodiment of the present inventioncomprises a duplex document scanning device comprising:

a) a document input support for holding a stack of document sheets to bescanned;

b) a document feed system for transporting document sheets to a documentscan region;

c) a document scanning system for scanning individual document sheetsduring movement thereof through said scan region;

d) a document output support for holding scanned document sheets;

e) a document delivery system for transporting scanned document sheetsfrom said scan region to said output support, said delivery systemincluding a driven roller, a pinch roller opposed to said driven rollerand defining a document transport nip therebetween, said driven rollerhaving a document contact surface which has a greater coefficient offriction than the coefficient of friction of the surface of the documentsheets to be transported; and

f) a drive arrangement for selectively rotating said driven roller inopposite directions.

A second embodiment of the invention provides a method of feeding andduplex scanning a document in a document scanning device comprising thesteps of:

a) transporting individual sheets of said document from a stack thereofto a scan region of a scanning system;

b) scanning a first face side of said document sheet at said scanregion;

c) transporting a leading edge of said sheet from said scan region intoa gap between a pair of spaced document delivery rollers;

d) moving said document delivery rollers together to grip opposite facesides of said sheet in a nip between said document delivery rollers androtating said document delivery rollers in a document delivery directionto pull said sheet therebetween and to move a trailing edge of saidsheet away from said scan region;

e) rotating said document delivery rollers in a feed direction beforesaid trailing edge of said sheet passes therebetween to feed and guidesaid sheet to said scan region in face inverted orientation for scanninga second face side of said sheet;

f) scanning said second face side of said sheet and transporting aleading edge of said sheet in a delivery direction toward said documentdelivery rollers before a trailing edge of said sheet passes said nipwhile moving in a feed direction;

g) separating said document delivery rollers from each other to form agap therebetween to permit said leading edge of said sheet to pass saidtrailing edge of said sheet during sheet movement between said documentdelivery rollers;

h) allowing said trailing edge of said sheet to pass between saidseparated document delivery rollers and then moving said rollerstogether to rotate said document delivery rollers in said documentdelivery direction to eject said sheet from between said documentdelivery rollers.

The apparatus aspects of the second embodiment of the invention providesa duplex document scanning device comprising:

a) a document input support for holding a stack of document sheets to bescanned;

b) a document feed system for transporting document sheets to a documentscan region;

c) a document scanning system for scanning individual document sheetsduring movement thereof through said scan region;

d) a document output support for holding scanned document sheets;

e) a document delivery system for transporting scanned document sheetsfrom said scan region to said output support, said delivery systemincluding a driven roller, a pinch roller opposed to and mounted formovement toward and away from said driven roller and defining a documenttransport nip therebetween;

f) a drive arrangement for selectively rotating said driven roller inopposite directions and for moving said pinch roller toward and awayfrom said driven roller; and

g) a gate for guiding movement of said sheet between said scan regionand said document delivery system.

In a third embodiment the present invention provides a method of feedingand duplex scanning a document in a document scanning device comprisingthe steps of:

a) transporting individual sheets of said document from a stack thereofto a scan region of a scanning system;

b) scanning a first face side of said document sheet at said scanregion;

c) transporting said sheet from said scan region to a first pair ofopposed document delivery rollers, said pair comprising a driven rollerand an opposed first pinch roller;

d) rotating said first pair of opposed document delivery rollers in adocument delivery direction;

e) causing a leading edge of said document sheet to engage a rotatingsheet edge guiding surface of said driven roller to move said leadingedge in engagement with said surface toward and to be gripped in a nipbetween said first pair of document delivery rollers to pull said sheettherebetween in a document delivery direction to move a trailing edge ofsaid sheet away from said scan region;

f) reversing the direction of rotation of said first pair of documentdelivery rollers to rotate said document delivery rollers in a documentfeed direction before said trailing edge of said sheet passestherebetween to feed said sheet to said scan region in face invertedorientation for scanning a second face side of said document sheet;

g) scanning said second face side of said sheet;

h) transporting a leading edge of said scanned sheet in said deliverydirection to engage said sheet edge guiding surface of said drivenroller to cause said leading edge to move toward and be gripped in a nipbetween a second pair of document transport rollers comprising saiddriven roller and an opposed second pinch roller; and

i) continuing rotation of said second pair of document delivery rollersin said exit direction to eject said sheet from between said second pairof document delivery rollers.

The apparatus aspects of the third embodiment provide a duplex documentscanning device comprising:

a) a document input support for holding a stack of document sheets to bescanned;

b) a document feed system for transporting document sheets from saiddocument input support to a document scan region;

c) a document scanning system for scanning individual document sheetsduring movement thereof through said scan region;

d) a document output support for holding scanned document sheets;

e) a document delivery system for transporting scanned document sheetsfrom said scan region to said output support, said delivery systemincluding a driven roller having a surface for engaging and moving theleading edge of a document sheet in the direction of rotation of saiddriven roller, a first pinch roller opposed to said driven roller anddefining a first document transport nip therebetween and a second pinchroller opposed to said driven roller and defining a second documenttransport nip therebetween; and

f) a drive arrangement for selectively rotating said driven roller inopposite directions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a through 1 j are sequential schematic side elevation crosssectional views of a document feeder according to the present inventionshowing progress of a duplex scanned document therethrough in accordancewith a first embodiment using document buckling and differentialslippage through opposed exit drive and pinch rollers.

FIGS. 2a through 2 f are sequential partial schematic side elevationviews of a second embodiment using a moveable pinch roller and adocument guide gate.

FIGS. 3a through 3 c are sequential partial schematic side elevationviews of a third embodiment using a three roller document transport withcrenellated center roller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Since the constructional details of the various aspects of documentscanning devices are well known, the present invention, being directedto the document delivery portion of such a device, i.e., that portionbeing downstream from the document scanning region, will be disclosedwith reference to various side elevational drawings shown in schematicform.

As seen in FIG. 1a and in the subsequent figures wherein like referencenumerals are used to designate like parts, the document scanning deviceincludes a document input support tray 10 which is preferably inclinedfrom the horizontal for gravitational assist in movement of individualdocument sheets from the input support tray 10 to a document feed system30. The scanning device also includes a document output support tray 20positioned as shown below the input support tray 10 for receiving andstacking scanned document sheets in an order which may be selected bythe device operator. For example, if a stack of individual documentsheets are to be simplex scanned, i.e., the source sheets bearinformation on one side only, the document sheets may be stacked face upon the input support tray 10 in numerical order, e.g., page 1 on top,with picking of individual sheets from the top of the stack so that thetop sheet is scanned first with the scanned sheets being inverted andejected onto the document output support tray 20 in face down order inthe same order in which they were scanned. Other stacking orders andorientations of the documents in either face up or face down orientationare possible as will follow.

The document feed system 30 delivers individual documents to be scannedto a scanning system 40 which includes a document wrap roller 42 orcylindrical path and one or more pinch rollers 44 disposed about theperiphery of the wrap roller 42 to hold individual document sheetsclosely in engagement therewith. The individual document sheets thusfollow the surface of the wrap roller to and through a scanning station49 at the left end of a platen 48. The specific details of the documentscanning portion of the scanning device are not pertinent to the presentinvention. An inclined document guide 46 extends from the scanningstation 49 direct the document sheets toward the document deliverysystem 50. Original document sheets to be scanned are fed by thedocument feed system 30 which may comprise a pre-feed or pick roller 32which transports the top sheet from the stack of documents to a pair ofactive single sheet separation rollers 34, 36 which convey the sheet tothe nip between the wrap roller 42 and pinch roller system 44. Althoughnot important to the details of the present invention, it will be seenthat a generally vertically extending stop 12 proximate the lower end ofthe document input support tray 10 operates in conjunction with a spring14 which biases the lower end of the support tray upwardly so that astack of documents thereon are abut the stop 12 with the top documentsheet being engageable by the friction surface of the pre-feed roller32. It will be further appreciated by persons skilled in the art thatreference throughout the present disclosure to the various rollers suchas the pre-feed roller 32 is intended to encompass arrangements wherethe roller constitutes a series of spaced rollers on a common shaft aswell as a single roller as seen in the schematic drawings.

Turning now to the document delivery system 50, in the embodiment seenin FIG. 1 the delivery system 50 is comprised of an upper pinch roller52 which is tangentially engaged with a lower driven roller 54 in theposition shown. A document guide and movement control gate 56 which maybe a flexible plastic gate of polyester sheet such as Mylar or the likeis mounted in the scanning device such that the gate 56 presents agenerally planar or flat surface extending from the nip between therollers 52, 54 toward the nip between the scanning wrap roller 42 andthe pinch roller 44. The lower end of the gate is moveable from theposition shown in FIG. 1a where it is positioned in the intended path ofmovement of the document sheet to the right (the document deliverydirection) from the scanning region 49 toward the nip between therollers 52, 54. The inherent flexibility of the gate 56 permits thelower end of the gate to be bent by engagement with the leading edge ofthe sheet up and out of the way as seen in FIG. 1c to permit the sheetto be received in the nip between the pinch roller 52 and the drivenroller 54. pinch roller 52 and the driven roller 54.

Progress of a document to be scanned using the first embodiment of thedocument delivery system 50 shown in FIGS. 1a-1 j will now be described.The first step of transporting a document sheet to be scanned from theinput support tray 10 through the scan region 49 involves separation ofthe first sheet of the document to be scanned from the remainder of thestack. This is accomplished in the document feed system 30 shown whichpicks the uppermost sheet from the document stack; however, there areknown systems that are capable of picking the lowermost sheet frombottom of the stack which could be used in the present invention ifdesired. To pick a single document sheet, the pre-feed roller 32 isrotated (clockwise as seen in FIG. 1a) to pass the document sheet overthe stop 12 to the nip between the active separation rollers 34, 36which insure that no more then a single document sheet is fed at a timeto the nip between the wrap roller 42 and pinch rollers 44. FIG. 1ashows the sheet being fed, the arrowhead pointing to the leftschematically indicating the leading edge of the sheet. FIG. 1b showsthe leading edge of the sheet having passed the wrap roller 42 and afterit has been scanned in the scan region 49. It will be noted that thetrailing edge of the sheet still has not passed entirely away from theinput support tray 10 past the pre-feed roller 32.

FIG. 1c shows the position of the document sheet after the scanning ofthe first (upper) face side thereof. It should be noted that the sheetis now in inverted relationship after having been passed once around thewrap roller 42. Note also the flexing of the gate 56 which has beenengaged by the leading edge of the moving document sheet and remains inthe bent position as seen in FIG. 1c. But, in comparison, FIGS. 1b and 1d show the gate in its normal unbent position in which it functions toguide a document sheet moving to the left as seen in FIG. 1e in a pathdelivery rollers 52, 54 (FIG. 1d) so that document is now once again,guided by gate 56, fed to the wrap roller 42.

FIG. 1f shows the scanning of the second side (originally the lowerside) of the document sheet as it once again passes around the wraproller 42 through the scanning region 49 and the leading edge of thedocument being directed toward the document delivery rollers 52, 54which continue to rotate in the document feed direction. Now, as theleading edge of the document sheet engages the rotating documentdelivery rollers as seen in FIG. 1g, sheet buckling is caused in theupper and lower reaches of the document sheet as shown. At this point, aportion of the second side of the document sheet has been scanned.Rotation of the document delivery rollers 50, 52 is again reversed asshown in FIG. 1h to consume all sheet buckle between the rollers suchthat both the leading and trailing edges of the document sheet are nowon the right side of the document delivery rollers 52, 54 as seen inFIG. 1h. Creating the buckle removes back tension in the sheet and thusallows the leading edge of the sheet to be easily grabbed by the nipbetween the delivery rollers 52, 54.

In FIG. 1i the lower driven roller 54 of the document delivery system 50continues to rotate in the document delivery direction but the directionof rotation of the upper pinch roller 52 has been reversed such thatroller 52 now rotates, due to frictional contact with the documentsheet, in the document delivery direction. This allows the documentsheet to differentially slide past itself, the leading or lower edge ofthe sheet moving to the right while the trailing edge of the document ispulled to the left so that the remainder of the second side of the sheetcan be scanned. This design feature and the designed in amount ofdifferential overlap between the two ends of the longer, e.g., legallength, document sheets to be scanned results in reduction of the totalsize and resulting footprint of the apparatus as compared with scanningdevices in which there is no sheet overlap in the scanning path. Thedifferential slippage in the first embodiment of the invention ispermitted by designing the document delivery driven roller 54 so that ithas a roughened document contact surface which has a greater coefficientof friction than the coefficient of friction between the facing surfacesof the individual document sheets to be scanned so that slippage takesplace between the opposed faces of the sheet rather than between thesheet and the driven roller 54. A suitable motor or motors andtransmission system or systems, not shown, provide rotary power to thepre-feed roller 32, the active separation rollers 34, 36, the wraproller 42 and the driven roller 54. The direction of rotation of thedriven roller 54 is selectively changed by a control system which iswell within the skill of persons skilled in the art and the details aretherefore not essential to a full understanding of the invention. Itwill also be appreciated that the gate 56 may comprise a passive gate ofpolyester sheet material or other flexible plastic with good memory asshown in the drawings in which the lower right end of the gate is bentby contact by the leading edge of a moving document sheet.Alternatively, the gate might take the form of a rigid pivotally mountedplanar member or a longitudinally slidable planar member; however,suitable electronic and mechanical control of gate movement addsunnecessary complexity to the preferred passive gate as described. FIG.1j shows ejection of the duplex scanned sheet to the output tray 20after completion of the scanning of the second side thereof.

The second embodiment of the document delivery system 60 is shown inFIGS. 2a-2 f and employs a driven roller 62 mounted below the documentdelivery path and an upper pinch roller 64 mounted for controlledmovement toward and away from the driven roller 62 to create a nip andgap therebetween as desired. The other elements of the document scanningdevice not shown in the embodiment seen in FIGS. 2a-2 f aresubstantially the same as seen in FIG. 1 including the document inputsupport tray 10 and document output tray 20, a suitable document feedsystem 30 and a document scanning system 40. FIG. 2a shows document feedfrom the guide 46 which is directed toward a gap between the drivenroller 62 and pinch roller 64 shown in the upper position as isindicated by the arrowhead in FIG. 2a to provide a gap for receivingwithout pinching the leading end of the scanned document. As seen inFIG. 2b, the pinch roller 64 is moved downwardly to its pinchingposition, the gate 56 being shown in flexed state, until the trailingedge of the document passes beyond the end of the flexed gate 56 butbefore it leaves the nip between the driven roller 62 and pinch roller64. The direction of rotation of the driven roller 62 is then reversedas seen in FIG. 2c to feed the document, guided by the unflexed gate 56,toward the upper portion of the wrap roller 42 for scanning of thesecond side of the document as seen in FIG. 2d. In FIG. 2e, the pinchroller 64 is again raised to create the gap between the drive roller andpinch roller 62 is for reception of the leading edge of the document,the flexed gate acting to hold the leading edge of the document againstthe surface of the driven roller 62 as it rotates in the documentdelivery direction (clockwise in FIG. 2e) while the upper reach of thedocument is free to move toward the left through the gap between therollers 62, 64. In FIG. 2f, the pinch roller 64 is again shown in itslowered position, the gate 56 is in its unflexed state, and the documentsheet may either be completely ejected for delivery onto the outputsupport tray 20 or the direction of rotation of the driven roller 62 mayagain be reversed to again feed the document to the wrap roller 42through the scanning region 49 for one further inversion of the documentsheet so that it can be stacked face down on the output support tray.Thus, a stack of document sheets can be scanned, one at a time, if theyare provided in original face-up relation in consecutive order from topto bottom of the stack so that they are delivered onto the output trayin face down orientation and in their original order. The designed inamount of overlap between the leading edge and trailing edge of thedocument sheet (for the longer documents, e.g., legal length, to bescanned) seen in FIG. 2e results in reduction of the footprint of theunit in the manner described with reference to the embodiment seen inFIGS. 1a-1 i.

A third embodiment of the document delivery system 70 is shown in FIGS.3a-3 c. Here again, the delivery and output support trays 10, 20, thedocument feed system 30 and the scanner itself are not shown althoughthey are of course required. In FIGS. 3a-3 c the delivery system 70includes a driven roller 72 having a peripheral sheet edge guidingsurface which may be crenellated or toothed or otherwise provided withradially extending grooves or troughs or a sufficiently roughenedsurface to catch and move the leading edge of the document to be scannedin the direction of rotation of the driven roller 72. A first pinchroller 74 above the driven roller 72 forms a nip with roller 72 forreceiving the leading edge of the scanned document sheet as shown inFIG. 3a. The dashed lines indicate the path of movement of the leadingedge of the scanned sheet from the scan region 49 generally toward thecenter of rotation of the roller 72 where the leading edge of the sheetwill engage and be received in one of the peripheral grooves to thustransport and position the sheet so that the leading edge will engageand be guided by the lower right end of the gate 56 into the nip betweenthe driven roller 72 and the upper pinch roller 74 in the sheet deliverydirection. In this embodiment the gate 56 may flex slightly upon contactwith the sheet as the leading edge is brought to the nip between rollers72 and 74.

In FIG. 3b, the direction of rotation of the driven roller 72 isreversed such that it now rotates in the sheet feed direction to movethe leading edge of the sheet, which has not been allowed to pass thenip between the roller 72, 74, back along the upper surface of the gate56 to the nip between the wrap roller 42 and the pinch roller 44 so thatsecond side of the sheet can be transported by the wrap roller 42through the scan region. Following scanning of the second side of thesheet, the leading edge is directed by the lower stationary guide 46 tothe nip formed between the driven roller 72 and the lower pinch roller76 whereby the scanned sheet may now be ejected from between thedelivery rollers 72, 76 onto the output support tray 20. In thisarrangement, the document sheet is scanned, inverted and scanned againbut cannot once again be inverted as in the preceding embodiments beforedelivery to the output tray 20. In the embodiment of FIGS. 3a-3 c, itwill again be noted that the trailing edge of the sheet and the leadingedge of a long sheet such as legal length overlap at the delivery system70 although, unlike the previous two embodiments, the leading edge isbetween one pinch roller 76 and the driven roller 72 and the trailingedge of the sheet is between the other pinch roller 74 and the drivenroller 72, thus resulting in reduction of the footprint size of the unitas described with reference to the first two embodiments of theinvention.

In all of the three embodiments of the document delivery system whichhave been described, it will be appreciated that stationary sheet guides46 may be used or not as desired in conjunction with or without apassive inherently flexible guide gate 56 or with a guide gate 56 whosemovement is controlled in timed relationship with the direction ofmovement of the sheets to be scanned. Leading and trailing edges of longsheets to be scanned overlap in the delivery system rollers and rollerreversal may be used to cause sheet buckling to conserve footprintspace.

Persons skilled in the art will appreciate that various modificationscan be made in the preferred embodiment shown and described above andthat the scope of protection is limited only by the wording of theclaims which follow.

What is claimed is:
 1. A duplex document scanning device comprising: a)a document input support for holding a stack of document sheets to bescanned; b) a document feed system for transporting document sheets to adocument scan region; c) a document scanning system for scanningindividual document sheets during movement thereof through said scanregion; d) a document output support for holding scanned documentsheets; e) a document delivery system for transporting scanned documentsheets from said scan region to said output support, said deliverysystem including a driven roller, a pinch roller opposed to said drivenroller and defining a document transport nip therebetween, said drivenroller having a document contact surface which has a greater coefficientof friction than the coefficient of friction of the surface of thedocument sheets to be transported; and f) a drive arrangement forselectively rotating said driven roller in opposite directions.
 2. Thedocument scanning device of claim 1, further comprising a gate forguiding movement of said sheet from said document delivery rollers tosaid scanning region.
 3. The document scanning device of claim 2,wherein said gate is a passive gate which is flexed due to contact ofsaid gate by a document sheet moving from said scan region toward saidnip in said delivery roller system.
 4. The document scanning device ofclaim 2, further comprising means for moving said gate from aninoperative position into an operative position to position said gate insheet guiding position between said scan region and said documentdelivery rollers when said document delivery rollers are driven in adocument delivery direction.
 5. A duplex document scanning devicecomprising: a) a document input support for holding a stack of documentsheets to be scanned; b) a document feed system for transportingdocument sheets to a document scan region; c) a document scanning systemfor scanning individual document sheets during movement thereof throughsaid scan region; d) a document output support for holding scanneddocument sheets; e) a document delivery system for transporting scanneddocument sheets from said scan region to said output support, saiddelivery system including a driven roller, a pinch roller opposed to andmounted for movement toward and away from said driven roller anddefining a document transport nip therebetween; f) a drive arrangementfor selectively rotating said driven roller in opposite directions andfor moving said pinch roller toward and away from said driven roller;and g) a gate for guiding movement of said sheet between said scanregion and said document delivery system.
 6. The document scanningdevice of claim 5, wherein said gate is a passive gate which is flexeddue to contact of said gate by a document sheet moving from scan regiontoward said nip in said document delivery system.
 7. The documentscanning device of claim 5, further comprising means for moving saidgate from an inoperative position into an operative position to positionsaid gate in sheet guiding position between said scan region and saiddocument delivery system when said document delivery rollers are drivenin a document delivery direction.
 8. The document scanning device ofclaim 5, further comprising a roller position controller for positioningsaid pinch roller in sheet gripping relationship with said driven rollerwhen a single thickness of a document sheet is between said rollers andfor positioning said pinch roller in sheet releasing position away fromsaid driven roller when a double thickness of said document sheet isbetween said exit rollers to permit sliding of said sheet past itselfbetween said rollers.
 9. A duplex document scanning device comprising:a) a document input support for holding a stack of document sheets to bescanned; b) a document feed system for transporting document sheets fromsaid document input support to a document scan region; c) a documentscanning system for scanning individual document sheets during movementthereof through said scan region; d) a document output support forholding scanned document sheets; e) a document delivery system fortransporting scanned document sheets from said scan region to saidoutput support, said delivery system including a driven roller having asurface for engaging and moving the leading edge of a document sheet inthe direction of rotation of said driven roller, a first pinch rolleropposed to said driven roller and defining a first document transportnip therebetween and a second pinch roller opposed to said driven rollerand defining a second document transport nip therebetween; and f) adrive arrangement for selectively rotating said driven roller inopposite directions.
 10. The document scanning device of claim 9,wherein said surface of said driven roller is crenellated and said pinchrollers are positioned on substantially diametrically opposite sides ofsaid driven roller for moving scanned document sheets in both documentfeed and delivery directions through said first nip and in a documentdelivery direction through said second nip.
 11. The document scanningdevice of claim 10, further comprising a gate for guiding movement ofsaid sheet from the nip between said first pinch roller and said drivenroller to said scanning system.
 12. The document scanning device ofclaim 11, wherein said gate is a passive gate which is flexed due tocontact of said gate by a document sheet moving from said scan regiontoward said first nip.
 13. The document scanning device of claim 11,further comprising means for moving said gate from an inoperativeposition into an operative position to position said gate in sheetguiding position between said scan region and said first nip when saiddocument delivery rollers are driven in a document delivery direction.